Study spells out x-ray
risk, not benefit
ABC Science Online,
Friday, 30 January 2004
The researchers calculated the lifetime risk of developing cancer from
having a diagnostic x-ray like this (FDA). X-rays may be responsible for
more than 400 cases of cancer in Australia a year, researchers have
estimated. But critics said these estimates were not balanced against the
benefits of x-rays, namely the early detection of treatable disease. Dr Amy
Berrington de González and Professor Sarah Darby from the U.K.'s University
of Oxford, estimated the risk of developing cancer from diagnostic medical
x-rays over a person's lifetime. These estimates, which appear in today's
issue of the journal The Lancet, formed part of the most detailed study of
its kind. The researchers compared data from 15 countries, including
Australia, and accounted for differences due to the type of cancer as well
as people's age and sex.
They estimated that x-rays were responsible for a 0.6-3.2% risk of
developing cancer during a person's lifetime. The risk depended on where
that person lived.
For Australians, they estimated that risk was 1.3%, which placed Australia
in the top four countries with the highest risk, along with Japan, Germany
and Croatia. That 1.3% risk was equivalent to an extra 431 cancer cases a
year in Australia, the researchers said. To calculate the risks, the U.K.
researchers calculated the amount of radiation each organ in the body would
be exposed to during an x-ray and computed tomography, or a CT scan. CT
scans use a series of x-ray images to create a three-dimensional image of
the inside of the body. The researchers also calculated the risk of
developing different types of cancer from radiation, based on the incidence
of cancer from survivors of the Japanese atomic bomb. The researchers
combined the radiation and cancer data to work out the lifetime risk and
number of cancers a year x-rays cause.
The U.K. and Poland had the lowest lifetime risk (0.6%) of developing cancer
due to having an x-ray. People in Japan had the highest risk (3.2%), which
the researchers said was down to x-rays being more commonly used in Japan
than in other countries. But x-rays were not widely used in Australia
compared with other countries, yet Australia had one of the highest risks.
The researchers did not explain this result.
Computed tomography scans use a series of x-ray images (FDA). CT scans were
responsible for the most cases of cancer, the researchers estimated. Barium
enemas used to view the large intestine, were also attributed to a higher
But German researchers Dr Peter Herzog and Dr Christina Rieger from the
Ludwig-Maximillians-University in Munich criticised the way the study was
designed in a commentary appearing in the same issue of journal. They also
criticised the researchers for not accounting for the benefits of using
"Benefits include the earlier detection of cancers by radiological
examinations and the possibility of early treatment, which probably allows
more cure of cancers than radiological exposure is able to cause," they
said. Using data from survivors of the Japanese atomic bomb may not have
been appropriate, they said, as survivors would have been exposed to other
types of radiation not used in x-rays. The U.K. researchers were aware of
the limitations of their own study. They assumed even small doses of
radiation could cause cancer and these low doses were as harmful as high
doses of radiation. "The possibility that we have overestimated the risks
cannot be ruled out," they said.